## Abstract

Nitrogen (N_{2}) may accumulate to unacceptable levels during closed-circuit anesthesia (CCA) when the sampled gases are redirected to the anesthesia circuit, because many gas analyzers entrain air as a reference gas to calibrate for oxygen analysis. Using oxygen instead of air as the reference gas for paramagnetic oxygen analysis could attenuate N_{2} accumulation. Forty-three adult ASA physical status I-III patients undergoing a variety of peripheral and abdominal procedures were assigned to one of two groups, depending on the reference gas used by a paramagnetic oxygen analyzer, either air (group I, n = 23) or oxygen (group II, n = 20). Gases sampled by the multigas analyzer were redirected to the anesthesia circuit. End-expired N_{2} (N(2 Et)) was calculated as 'balance gas': (100 - %O_{2} - %anesthetic vapor - %CO_{2}). N(2 Et) after 55 min (N(2 Et 55 min)) was correlated with the end-expired N_{2} concentration when the circuit was closed (N(2 Et 0 min)) and 5 min (N(2 Et 5 min)) thereafter. In group I, N(2 Et) accumulated almost linearly over time (t, min): N(2 Et) (%) = 2.47 + 0.61 * t (r^{2} = 0.999). N(2 Et 0 min), N(2 Et 5 min), and N(2 Et 55 min) were 1.3 ± 0.8, 5.3 ± 1.7, and 35.3 ± 5.3%, respectively (mean ± SD). The correlation (r^{2}) between N(2 Et 55 min) and N(2 Et 0 min) was 0.19, and between N(2 Et 55 min) and N(2 Et 5 min) it was 0.56. In group II, N(2 Et) increased exponentially: N(2 Et) (%) = 1.01 + 11.9 * (1 - e(-t/43.5)) (r^{2} = 0.99). N(2 Et 0 min), N(2 Et 5 min), and N(2 Et 55 min) were 0.87 ± 0.93, 2.6 ± 1.5, and 10.1 ± 2.9%, respectively. The correlation (r^{2}) between N(2 Et 55 min) and N(2 Et 0 min) was 0.04, and between N(2 Et 55 min) and N(2 Et 5 min) it was 0.40. We conclude that paramagnetic oxygen analyzers that use oxygen as the reference gas significantly attenuate N_{2} accumulation during CCA, which may reduce the need for frequent flushing of the anesthesia system, may provide more constant oxygen and nitrous oxide concentrations, and may simplify pharmacokinetic studies of potent inhaled anesthetics.

Original language | English (US) |
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Pages (from-to) | 381-384 |

Number of pages | 4 |

Journal | Journal of Clinical Monitoring and Computing |

Volume | 14 |

Issue number | 6 |

DOIs | |

State | Published - Aug 1998 |

## Keywords

- Closed-circuit anesthesia
- Equipment
- Multigas analyzer
- Nitrogen accumulation
- Oxygen analyzer

## ASJC Scopus subject areas

- Health Informatics
- Critical Care and Intensive Care Medicine
- Anesthesiology and Pain Medicine